gtk2/gtk/gtktextiter.c

/* GTK - The GIMP Toolkit
 * gtktextiter.c Copyright (C) 2000 Red Hat, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

/*
 * Modified by the GTK+ Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GTK+ Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GTK+ at ftp://ftp.gtk.org/pub/gtk/.
 */

#include "gtktextiter.h"
#include "gtktextbtree.h"
#include "gtktextiterprivate.h"
#include "gtkdebug.h"
#include <string.h>
#include <ctype.h>

typedef struct _GtkTextRealIter GtkTextRealIter;

struct _GtkTextRealIter
{
  /* Always-valid information */
  GtkTextBTree *tree;
  GtkTextLine *line;
  /* At least one of these is always valid;
     if invalid, they are -1.

     If the line byte offset is valid, so is the segment byte offset;
     and ditto for char offsets. */
  gint line_byte_offset;
  gint line_char_offset;
  /* These two are valid if >= 0 */
  gint cached_char_index;
  gint cached_line_number;
  /* Stamps to detect the buffer changing under us */
  gint chars_changed_stamp;
  gint segments_changed_stamp;
  /* Valid if the segments_changed_stamp is up-to-date */
  GtkTextLineSegment *segment;     /* indexable segment we index */
  GtkTextLineSegment *any_segment; /* first segment in our location,
                                      maybe same as "segment" */
  /* One of these will always be valid if segments_changed_stamp is
     up-to-date. If invalid, they are -1.

     If the line byte offset is valid, so is the segment byte offset;
     and ditto for char offsets. */
  gint segment_byte_offset;
  gint segment_char_offset;
};

/* These "set" functions should not assume any fields
   other than the char stamp and the tree are valid.
*/
static void
iter_set_common (GtkTextRealIter *iter,
                 GtkTextLine *line)
{
  /* Update segments stamp */
  iter->segments_changed_stamp =
    gtk_text_btree_get_segments_changed_stamp (iter->tree);

  iter->line = line;

  iter->line_byte_offset = -1;
  iter->line_char_offset = -1;
  iter->segment_byte_offset = -1;
  iter->segment_char_offset = -1;
  iter->cached_char_index = -1;
  iter->cached_line_number = -1;
}

static void
iter_set_from_byte_offset (GtkTextRealIter *iter,
                           GtkTextLine *line,
                           gint byte_offset)
{
  iter_set_common (iter, line);

  gtk_text_line_byte_locate (iter->line,
                             byte_offset,
                             &iter->segment,
                             &iter->any_segment,
                             &iter->segment_byte_offset,
                             &iter->line_byte_offset);

}

static void
iter_set_from_char_offset (GtkTextRealIter *iter,
                           GtkTextLine *line,
                           gint char_offset)
{
  iter_set_common (iter, line);

  gtk_text_line_char_locate (iter->line,
                             char_offset,
                             &iter->segment,
                             &iter->any_segment,
                             &iter->segment_char_offset,
                             &iter->line_char_offset);
}

static void
iter_set_from_segment (GtkTextRealIter *iter,
                       GtkTextLine *line,
                       GtkTextLineSegment *segment)
{
  GtkTextLineSegment *seg;
  gint byte_offset;

  /* This could theoretically be optimized by computing all the iter
     fields in this same loop, but I'm skipping it for now. */
  byte_offset = 0;
  seg = line->segments;
  while (seg != segment)
    {
      byte_offset += seg->byte_count;
      seg = seg->next;
    }

  iter_set_from_byte_offset (iter, line, byte_offset);
}

/* This function ensures that the segment-dependent information is
   truly computed lazily; often we don't need to do the full make_real
   work. This ensures the btree and line are valid, but doesn't
   update the segments. */
static GtkTextRealIter*
gtk_text_iter_make_surreal (const GtkTextIter *_iter)
{
  GtkTextRealIter *iter = (GtkTextRealIter*)_iter;

  if (iter->chars_changed_stamp !=
      gtk_text_btree_get_chars_changed_stamp (iter->tree))
    {
      g_warning ("Invalid text buffer iterator: either the iterator "
                 "is uninitialized, or the characters/pixbufs/widgets "
                 "in the buffer have been modified since the iterator "
                 "was created.\nYou must use marks, character numbers, "
                 "or line numbers to preserve a position across buffer "
                 "modifications.\nYou can apply tags and insert marks "
                 "without invalidating your iterators,\n"
                 "but any mutation that affects 'indexable' buffer contents "
                 "(contents that can be referred to by character offset)\n"
                 "will invalidate all outstanding iterators");
      return NULL;
    }

  /* We don't update the segments information since we are becoming
     only surreal. However we do invalidate the segments information
     if appropriate, to be sure we segfault if we try to use it and we
     should have used make_real. */

  if (iter->segments_changed_stamp !=
      gtk_text_btree_get_segments_changed_stamp (iter->tree))
    {
      iter->segment = NULL;
      iter->any_segment = NULL;
      /* set to segfault-causing values. */
      iter->segment_byte_offset = -10000;
      iter->segment_char_offset = -10000;
    }

  return iter;
}

static GtkTextRealIter*
gtk_text_iter_make_real (const GtkTextIter *_iter)
{
  GtkTextRealIter *iter;

  iter = gtk_text_iter_make_surreal (_iter);

  if (iter->segments_changed_stamp !=
      gtk_text_btree_get_segments_changed_stamp (iter->tree))
    {
      if (iter->line_byte_offset >= 0)
        {
          iter_set_from_byte_offset (iter,
                                     iter->line,
                                     iter->line_byte_offset);
        }
      else
        {
          g_assert (iter->line_char_offset >= 0);

          iter_set_from_char_offset (iter,
                                     iter->line,
                                     iter->line_char_offset);
        }
    }

  g_assert (iter->segment != NULL);
  g_assert (iter->any_segment != NULL);
  g_assert (iter->segment->char_count > 0);

  return iter;
}

static GtkTextRealIter*
iter_init_common (GtkTextIter *_iter,
                  GtkTextBTree *tree)
{
  GtkTextRealIter *iter = (GtkTextRealIter*)_iter;

  g_return_val_if_fail (iter != NULL, NULL);
  g_return_val_if_fail (tree != NULL, NULL);

  iter->tree = tree;

  iter->chars_changed_stamp =
    gtk_text_btree_get_chars_changed_stamp (iter->tree);

  return iter;
}

static GtkTextRealIter*
iter_init_from_segment (GtkTextIter *iter,
                        GtkTextBTree *tree,
                        GtkTextLine *line,
                        GtkTextLineSegment *segment)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_segment (real, line, segment);

  return real;
}

static GtkTextRealIter*
iter_init_from_byte_offset (GtkTextIter *iter,
                            GtkTextBTree *tree,
                            GtkTextLine *line,
                            gint line_byte_offset)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_byte_offset (real, line, line_byte_offset);

  return real;
}

static GtkTextRealIter*
iter_init_from_char_offset (GtkTextIter *iter,
                            GtkTextBTree *tree,
                            GtkTextLine *line,
                            gint line_char_offset)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (line != NULL, NULL);

  real = iter_init_common (iter, tree);

  iter_set_from_char_offset (real, line, line_char_offset);

  return real;
}

static inline void
invalidate_segment (GtkTextRealIter *iter)
{
  iter->segments_changed_stamp -= 1;
}

static inline void
invalidate_char_index (GtkTextRealIter *iter)
{
  iter->cached_char_index = -1;
}

static inline void
invalidate_line_number (GtkTextRealIter *iter)
{
  iter->cached_line_number = -1;
}

static inline void
adjust_char_index (GtkTextRealIter *iter, gint count)
{
  if (iter->cached_char_index >= 0)
    iter->cached_char_index += count;
}

static inline void
adjust_line_number (GtkTextRealIter *iter, gint count)
{
  if (iter->cached_line_number >= 0)
    iter->cached_line_number += count;
}

static inline void
adjust_char_offsets (GtkTextRealIter *iter, gint count)
{
  if (iter->line_char_offset >= 0)
    {
      iter->line_char_offset += count;
      g_assert (iter->segment_char_offset >= 0);
      iter->segment_char_offset += count;
    }
}

static inline void
adjust_byte_offsets (GtkTextRealIter *iter, gint count)
{
  if (iter->line_byte_offset >= 0)
    {
      iter->line_byte_offset += count;
      g_assert (iter->segment_byte_offset >= 0);
      iter->segment_byte_offset += count;
    }
}

static inline void
ensure_char_offsets (GtkTextRealIter *iter)
{
  if (iter->line_char_offset < 0)
    {
      g_assert (iter->line_byte_offset >= 0);

      gtk_text_line_byte_to_char_offsets (iter->line,
                                          iter->line_byte_offset,
                                          &iter->line_char_offset,
                                          &iter->segment_char_offset);
    }
}

static inline void
ensure_byte_offsets (GtkTextRealIter *iter)
{
  if (iter->line_byte_offset < 0)
    {
      g_assert (iter->line_char_offset >= 0);

      gtk_text_line_char_to_byte_offsets (iter->line,
                                          iter->line_char_offset,
                                          &iter->line_byte_offset,
                                          &iter->segment_byte_offset);
    }
}

static inline gboolean
is_segment_start (GtkTextRealIter *real)
{
  return real->segment_byte_offset == 0 || real->segment_char_offset == 0;
}

#if 1
static void
check_invariants (const GtkTextIter *iter)
{
  if (gtk_debug_flags & GTK_DEBUG_TEXT)
    gtk_text_iter_check (iter);
}
#else
#define check_invariants (x)
#endif

/**
 * gtk_text_iter_get_buffer:
 * @iter: an iterator
 *
 * Return the #GtkTextBuffer this iterator is associated with
 *
 * Return value: the buffer
 **/
GtkTextBuffer*
gtk_text_iter_get_buffer (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  return gtk_text_btree_get_buffer (real->tree);
}

/**
 * gtk_text_iter_copy:
 * @iter: an iterator
 *
 * Create a dynamically-allocated copy of an iterator. This function
 * is not useful in applications, because iterators can be copied with a
 * simple assignment (<literal>GtkTextIter i = j;</literal>). The
 * function is used by language bindings.
 *
 * Return value: a copy of the @iter, free with gtk_text_iter_free ()
 **/
GtkTextIter*
gtk_text_iter_copy (const GtkTextIter *iter)
{
  GtkTextIter *new_iter;

  g_return_val_if_fail (iter != NULL, NULL);

  new_iter = g_new (GtkTextIter, 1);

  *new_iter = *iter;

  return new_iter;
}

/**
 * gtk_text_iter_free:
 * @iter: a dynamically-allocated iterator
 *
 * Free an iterator allocated on the heap. This function
 * is intended for use in language bindings, and is not
 * especially useful for applications, because iterators can
 * simply be allocated on the stack.
 *
 **/
void
gtk_text_iter_free (GtkTextIter *iter)
{
  g_return_if_fail (iter != NULL);

  g_free (iter);
}

GtkTextLineSegment*
gtk_text_iter_get_indexable_segment (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  g_assert (real->segment != NULL);

  return real->segment;
}

GtkTextLineSegment*
gtk_text_iter_get_any_segment (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  g_assert (real->any_segment != NULL);

  return real->any_segment;
}

gint
gtk_text_iter_get_segment_byte (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_byte_offsets (real);

  check_invariants (iter);

  return real->segment_byte_offset;
}

gint
gtk_text_iter_get_segment_char (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  return real->segment_char_offset;
}

/* This function does not require a still-valid
   iterator */
GtkTextLine*
gtk_text_iter_get_text_line (const GtkTextIter *iter)
{
  const GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = (const GtkTextRealIter*)iter;

  return real->line;
}

/* This function does not require a still-valid
   iterator */
GtkTextBTree*
gtk_text_iter_get_btree (const GtkTextIter *iter)
{
  const GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = (const GtkTextRealIter*)iter;

  return real->tree;
}

/*
 * Conversions
 */

/**
 * gtk_text_iter_get_offset:
 * @iter: an iterator
 *
 * Returns the character offset of an iterator.
 * Each character in a #GtkTextBuffer has an offset,
 * starting with 0 for the first character in the buffer.
 * Use gtk_text_buffer_get_iter_at_offset () to convert an
 * offset back into an iterator.
 *
 * Return value: a character offset
 **/
gint
gtk_text_iter_get_offset (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);
  
  if (real->cached_char_index < 0)
    {
      ensure_char_offsets (real);
      
      real->cached_char_index =
        gtk_text_line_char_index (real->line);
      real->cached_char_index += real->line_char_offset;
    }

  check_invariants (iter);

  return real->cached_char_index;
}

/**
 * gtk_text_iter_get_line:
 * @iter: an iterator
 *
 * Returns the line number containing the iterator. Lines in
 * a #GtkTextBuffer are numbered beginning with 0 for the first
 * line in the buffer.
 *
 * Return value: a line number
 **/
gint
gtk_text_iter_get_line (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  if (real->cached_line_number < 0)
    real->cached_line_number =
      gtk_text_line_get_number (real->line);

  check_invariants (iter);

  return real->cached_line_number;
}

/**
 * gtk_text_iter_get_line_offset:
 * @iter: an iterator
 *
 * Returns the character offset of the iterator,
 * counting from the start of a newline-terminated line.
 * The first character on the line has offset 0.
 *
 * Return value: offset from start of line
 **/
gint
gtk_text_iter_get_line_offset (const GtkTextIter *iter)
{

  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  ensure_char_offsets (real);

  check_invariants (iter);

  return real->line_char_offset;
}

/**
 * gtk_text_iter_get_line_index:
 * @iter: an iterator
 *
 * Returns the byte index of the iterator, counting
 * from the start of a newline-terminated line.
 * Remember that #GtkTextBuffer encodes text in
 * UTF-8, and that characters can require a variable
 * number of bytes to represent.
 *
 * Return value: distance from start of line, in bytes
 **/
gint
gtk_text_iter_get_line_index (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  ensure_byte_offsets (real);

  check_invariants (iter);

  return real->line_byte_offset;
}

/*
 * Dereferencing
 */

/**
 * gtk_text_iter_get_char:
 * @iter: an iterator
 *
 * Returns the Unicode character at this iterator.  (Equivalent to
 * operator* on a C++ iterator.)  If the iterator points at a
 * non-character element, such as an image embedded in the buffer, the
 * Unicode "unknown" character 0xFFFD is returned. If invoked on
 * the end iterator, zero is returned; zero is not a valid Unicode character.
 * So you can write a loop which ends when gtk_text_iter_get_char ()
 * returns 0.
 *
 * Return value: a Unicode character, or 0 if @iter is not dereferenceable
 **/
gunichar
gtk_text_iter_get_char (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, 0);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);

  if (gtk_text_iter_is_last (iter))
    return 0;
  else if (real->segment->type == &gtk_text_char_type)
    {
      ensure_byte_offsets (real);
      
      return g_utf8_get_char (real->segment->body.chars +
                              real->segment_byte_offset);
    }
  else
    {
      /* Unicode "unknown character" 0xFFFD */
      return gtk_text_unknown_char;
    }
}

/**
 * gtk_text_iter_get_slice:
 * @start: iterator at start of a range
 * @end: iterator at end of a range
 *
 * Returns the text in the given range. A "slice" is an array of
 * characters encoded in UTF-8 format, including the Unicode "unknown"
 * character 0xFFFD for iterable non-character elements in the buffer,
 * such as images.  Because images are encoded in the slice, byte and
 * character offsets in the returned array will correspond to byte
 * offsets in the text buffer. Note that 0xFFFD can occur in normal
 * text as well, so it is not a reliable indicator that a pixbuf or
 * widget is in the buffer.
 *
 * Return value: slice of text from the buffer
 **/
gchar*
gtk_text_iter_get_slice       (const GtkTextIter *start,
                               const GtkTextIter *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return gtk_text_btree_get_text (start, end, TRUE, TRUE);
}

/**
 * gtk_text_iter_get_text:
 * @start: iterator at start of a range
 * @end: iterator at end of a range
 *
 * Returns <emphasis>text</emphasis> in the given range.  If the range
 * contains non-text elements such as images, the character and byte
 * offsets in the returned string will not correspond to character and
 * byte offsets in the buffer. If you want offsets to correspond, see
 * gtk_text_iter_get_slice ().
 *
 * Return value: array of characters from the buffer
 **/
gchar*
gtk_text_iter_get_text       (const GtkTextIter *start,
                              const GtkTextIter *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return gtk_text_btree_get_text (start, end, TRUE, FALSE);
}

/**
 * gtk_text_iter_get_visible_slice:
 * @start: iterator at start of range
 * @end: iterator at end of range
 *
 * Like gtk_text_iter_get_slice (), but invisible text is not included.
 * Invisible text is usually invisible because a #GtkTextTag with the
 * "invisible" attribute turned on has been applied to it.
 *
 * Return value: slice of text from the buffer
 **/
gchar*
gtk_text_iter_get_visible_slice (const GtkTextIter  *start,
                                 const GtkTextIter  *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return gtk_text_btree_get_text (start, end, FALSE, TRUE);
}

/**
 * gtk_text_iter_get_visible_text:
 * @start: iterator at start of range
 * @end: iterator at end of range
 *
 * Like gtk_text_iter_get_text (), but invisible text is not included.
 * Invisible text is usually invisible because a #GtkTextTag with the
 * "invisible" attribute turned on has been applied to it.
 *
 * Return value: string containing visible text in the range
 **/
gchar*
gtk_text_iter_get_visible_text (const GtkTextIter  *start,
                                const GtkTextIter  *end)
{
  g_return_val_if_fail (start != NULL, NULL);
  g_return_val_if_fail (end != NULL, NULL);

  check_invariants (start);
  check_invariants (end);

  return gtk_text_btree_get_text (start, end, FALSE, FALSE);
}

/**
 * gtk_text_iter_get_pixbuf:
 * @iter: an iterator
 *
 * If the location pointed to by @iter contains a pixbuf, the pixbuf
 * is returned (with no new reference count added). Otherwise,
 * NULL is returned.
 *
 * Return value: the pixbuf at @iter
 **/
GdkPixbuf*
gtk_text_iter_get_pixbuf (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  if (real->segment->type != &gtk_text_pixbuf_type)
    return NULL;
  else
    return real->segment->body.pixbuf.pixbuf;
}

/**
 * gtk_text_iter_get_child_anchor:
 * @iter: an iterator
 *
 * If the location pointed to by @iter contains a child anchor, the
 * anchor is returned (with no new reference count added). Otherwise,
 * NULL is returned.
 *
 * Return value: the anchor at @iter
 **/
GtkTextChildAnchor*
gtk_text_iter_get_child_anchor (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  if (real->segment->type != &gtk_text_child_type)
    return NULL;
  else
    return real->segment->body.child.obj;
}

/**
 * gtk_text_iter_get_marks:
 * @iter: an iterator
 *
 * Returns a list of all #GtkTextMark at this location. Because marks
 * are not iterable (they don't take up any "space" in the buffer,
 * they are just marks in between iterable locations), multiple marks
 * can exist in the same place. The returned list is not in any
 * meaningful order.
 *
 * Return value: list of #GtkTextMark
 **/
GSList*
gtk_text_iter_get_marks (const GtkTextIter *iter)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GSList *retval;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  retval = NULL;
  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_left_mark_type ||
          seg->type == &gtk_text_right_mark_type)
        retval = g_slist_prepend (retval, seg->body.mark.obj);

      seg = seg->next;
    }

  /* The returned list isn't guaranteed to be in any special order,
     and it isn't. */
  return retval;
}

/**
 * gtk_text_iter_get_toggled_tags:
 * @iter: an iterator
 * @toggled_on: TRUE to get toggled-on tags
 *
 * Returns a list of #GtkTextTag that are toggled on or off at this
 * point.  (If @toggled_on is TRUE, the list contains tags that are
 * toggled on.) If a tag is toggled on at @iter, then some non-empty
 * range of characters following @iter has that tag applied to it.  If
 * a tag is toggled off, then some non-empty range following @iter
 * does <emphasis>not</emphasis> have the tag applied to it.
 *
 * Return value: tags toggled at this point
 **/
GSList*
gtk_text_iter_get_toggled_tags  (const GtkTextIter  *iter,
                                 gboolean            toggled_on)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GSList *retval;

  g_return_val_if_fail (iter != NULL, NULL);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return NULL;

  check_invariants (iter);

  retval = NULL;
  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (toggled_on)
        {
          if (seg->type == &gtk_text_toggle_on_type)
            {
              retval = g_slist_prepend (retval, seg->body.toggle.info->tag);
            }
        }
      else
        {
          if (seg->type == &gtk_text_toggle_off_type)
            {
              retval = g_slist_prepend (retval, seg->body.toggle.info->tag);
            }
        }

      seg = seg->next;
    }

  /* The returned list isn't guaranteed to be in any special order,
     and it isn't. */
  return retval;
}

/**
 * gtk_text_iter_begins_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * Returns TRUE if @tag is toggled on at exactly this point. If @tag
 * is NULL, returns TRUE if any tag is toggled on at this point. Note
 * that the gtk_text_iter_begins_tag () returns TRUE if @iter is the
 * <emphasis>start</emphasis> of the tagged range;
 * gtk_text_iter_has_tag () tells you whether an iterator is
 * <emphasis>within</emphasis> a tagged range.
 *
 * Return value: whether @iter is the start of a range tagged with @tag
 **/
gboolean
gtk_text_iter_begins_tag    (const GtkTextIter  *iter,
                             GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_toggle_on_type)
        {
          if (tag == NULL ||
              seg->body.toggle.info->tag == tag)
            return TRUE;
        }

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_ends_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * Returns TRUE if @tag is toggled off at exactly this point. If @tag
 * is NULL, returns TRUE if any tag is toggled off at this point. Note
 * that the gtk_text_iter_ends_tag () returns TRUE if @iter is the
 * <emphasis>end</emphasis> of the tagged range;
 * gtk_text_iter_has_tag () tells you whether an iterator is
 * <emphasis>within</emphasis> a tagged range.
 *
 * Return value: whether @iter is the end of a range tagged with @tag
 *
 **/
gboolean
gtk_text_iter_ends_tag   (const GtkTextIter  *iter,
                          GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if (seg->type == &gtk_text_toggle_off_type)
        {
          if (tag == NULL ||
              seg->body.toggle.info->tag == tag)
            return TRUE;
        }

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_toggles_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag, or NULL
 *
 * This is equivalent to (gtk_text_iter_begins_tag () ||
 * gtk_text_iter_ends_tag ()), i.e. it tells you whether a range with
 * @tag applied to it begins <emphasis>or</emphasis> ends at @iter.
 *
 * Return value: whether @tag is toggled on or off at @iter
 **/
gboolean
gtk_text_iter_toggles_tag       (const GtkTextIter  *iter,
                                 GtkTextTag         *tag)
{
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  seg = real->any_segment;
  while (seg != real->segment)
    {
      if ( (seg->type == &gtk_text_toggle_off_type ||
            seg->type == &gtk_text_toggle_on_type) &&
           (tag == NULL ||
            seg->body.toggle.info->tag == tag) )
        return TRUE;

      seg = seg->next;
    }

  return FALSE;
}

/**
 * gtk_text_iter_has_tag:
 * @iter: an iterator
 * @tag: a #GtkTextTag
 *
 * Returns TRUE if @iter is within a range tagged with @tag.
 *
 * Return value: whether @iter is tagged with @tag
 **/
gboolean
gtk_text_iter_has_tag           (const GtkTextIter   *iter,
                                 GtkTextTag          *tag)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (GTK_IS_TEXT_TAG (tag), FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_byte_offset >= 0)
    {
      return gtk_text_line_byte_has_tag (real->line, real->tree,
                                         real->line_byte_offset, tag);
    }
  else
    {
      g_assert (real->line_char_offset >= 0);
      return gtk_text_line_char_has_tag (real->line, real->tree,
                                         real->line_char_offset, tag);
    }
}

/**
 * gtk_text_iter_get_tags:
 * @iter: a #GtkTextIter
 * 
 * Returns a list of tags that apply to @iter, in ascending order of
 * priority (highest-priority tags are last). The #GtkTextTag in the
 * list don't have a reference added, but you have to free the list
 * itself.
 * 
 * Return value: list of #GtkTextTag
 **/
GSList*
gtk_text_iter_get_tags (const GtkTextIter *iter)
{
  GtkTextTag** tags;
  gint tag_count = 0;
  gint i;
  GSList *retval;
  
  g_return_val_if_fail (iter != NULL, NULL);
  
  /* Get the tags at this spot */
  tags = gtk_text_btree_get_tags (iter, &tag_count);

  /* No tags, use default style */
  if (tags == NULL || tag_count == 0)
    {
      if (tags)
        g_free (tags);

      return NULL;
    }

  /* Sort tags in ascending order of priority */
  gtk_text_tag_array_sort (tags, tag_count);

  retval = NULL;
  i = 0;
  while (i < tag_count)
    {
      retval = g_slist_prepend (retval, tags[i]);
      ++i;
    }
  
  g_free (tags);

  /* Return tags in ascending order of priority */
  return g_slist_reverse (retval);
}

/**
 * gtk_text_iter_editable:
 * @iter: an iterator
 * @default_setting: TRUE if text is editable by default
 *
 * Returns whether @iter is within an editable region of text.
 * Non-editable text is "locked" and can't be changed by the user via
 * #GtkTextView. This function is simply a convenience wrapper around
 * gtk_text_iter_get_attributes (). If no tags applied to this text
 * affect editability, @default_setting will be returned.
 *
 * Return value: whether @iter is inside an editable range
 **/
gboolean
gtk_text_iter_editable (const GtkTextIter *iter,
                        gboolean           default_setting)
{
  GtkTextAttributes *values;
  gboolean retval;

  values = gtk_text_attributes_new ();

  values->editable = default_setting;

  gtk_text_iter_get_attributes (iter, values);

  retval = values->editable;

  gtk_text_attributes_unref (values);

  return retval;
}

/**
 * gtk_text_iter_get_language:
 * @iter: an iterator
 *
 * A convenience wrapper around gtk_text_iter_get_attributes (),
 * which returns the language in effect at @iter. If no tags affecting
 * language * apply to @iter, the return value is identical to that of
 * gtk_get_default_language ().
 *
 * Return value: language in effect at @iter
 **/
static gchar*
gtk_text_iter_get_language (const GtkTextIter *iter)
{
  GtkTextAttributes *values;
  gchar *retval;

  values = gtk_text_attributes_new ();

  gtk_text_iter_get_attributes (iter, values);

  retval = g_strdup (values->language);

  gtk_text_attributes_unref (values);

  return retval;
}

/**
 * gtk_text_iter_starts_line:
 * @iter: an iterator
 *
 * Returns TRUE if @iter begins a newline-terminated line,
 * i.e. gtk_text_iter_get_line_offset () would return 0.
 * However this function is potentially more efficient than
 * gtk_text_iter_get_line_offset () because it doesn't have to compute
 * the offset, it just has to see whether it's 0.
 *
 * Return value: whether @iter begins a line
 **/
gboolean
gtk_text_iter_starts_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_byte_offset >= 0)
    {
      return (real->line_byte_offset == 0);
    }
  else
    {
      g_assert (real->line_char_offset >= 0);
      return (real->line_char_offset == 0);
    }
}

/**
 * gtk_text_iter_ends_line:
 * @iter: an iterator
 *
 * Returns TRUE if @iter points to a newline character.
 *
 * Return value: whether @iter is at the end of a line
 **/
gboolean
gtk_text_iter_ends_line (const GtkTextIter   *iter)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  check_invariants (iter);

  return gtk_text_iter_get_char (iter) == '\n';
}

/**
 * gtk_text_iter_is_last:
 * @iter: an iterator
 *
 * Returns TRUE if @iter is the end iterator, i.e. one past the last
 * dereferenceable iterator in the buffer. gtk_text_iter_is_last () is
 * the most efficient way to check whether an iterator is the end
 * iterator.
 *
 * Return value: whether @iter is the end iterator
 **/
gboolean
gtk_text_iter_is_last (const GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  return gtk_text_line_is_last (real->line, real->tree);
}

/**
 * gtk_text_iter_is_first:
 * @iter: an iterator
 *
 * Returns TRUE if @iter is the first iterator in the buffer, that is
 * if @iter has a character offset of 0.
 *
 * Return value: whether @iter is the first in the buffer
 **/
gboolean
gtk_text_iter_is_first (const GtkTextIter *iter)
{
  return gtk_text_iter_get_offset (iter) == 0;
}

/**
 * gtk_text_iter_get_chars_in_line:
 * @iter: an iterator
 *
 * Returns the number of characters in the line containing @iter,
 * including the terminating newline.
 *
 * Return value: number of characters in the line
 **/
gint
gtk_text_iter_get_chars_in_line (const GtkTextIter   *iter)
{
  GtkTextRealIter *real;
  gint count;
  GtkTextLineSegment *seg;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return 0;

  check_invariants (iter);

  if (real->line_char_offset >= 0)
    {
      /* We can start at the segments we've already found. */
      count = real->line_char_offset - real->segment_char_offset;
      seg = gtk_text_iter_get_indexable_segment (iter);
    }
  else
    {
      /* count whole line. */
      seg = real->line->segments;
      count = 0;
    }


  while (seg != NULL)
    {
      count += seg->char_count;

      seg = seg->next;
    }

  return count;
}

/**
 * gtk_text_iter_get_attributes:
 * @iter: an iterator
 * @values: a #GtkTextAttributes to be filled in
 *
 * Computes the effect of any tags applied to this spot in the
 * text. The @values parameter should be initialized to the default
 * settings you wish to use if no tags are in effect.
 * gtk_text_iter_get_attributes () will modify @values, applying the
 * effects of any tags present at @iter. If any tags affected @values,
 * the function returns TRUE.
 *
 * Return value: TRUE if @values was modified
 **/
gboolean
gtk_text_iter_get_attributes (const GtkTextIter  *iter,
                              GtkTextAttributes *values)
{
  GtkTextTag** tags;
  gint tag_count = 0;

  /* Get the tags at this spot */
  tags = gtk_text_btree_get_tags (iter, &tag_count);

  /* No tags, use default style */
  if (tags == NULL || tag_count == 0)
    {
      if (tags)
        g_free (tags);

      return FALSE;
    }

  /* Sort tags in ascending order of priority */
  gtk_text_tag_array_sort (tags, tag_count);

  gtk_text_attributes_fill_from_tags (values,
                                      tags,
                                      tag_count);

  g_free (tags);

  return TRUE;
}

/*
 * Increments/decrements
 */

/* The return value of this indicates WHETHER WE MOVED.
 * The return value of public functions indicates
 * (MOVEMENT OCCURRED && NEW ITER IS DEREFERENCEABLE)
 */
static gboolean
forward_line_leaving_caches_unmodified (GtkTextRealIter *real)
{
  GtkTextLine *new_line;

  new_line = gtk_text_line_next (real->line);

  g_assert (new_line != real->line);

  if (new_line != NULL)
    {
      real->line = new_line;

      real->line_byte_offset = 0;
      real->line_char_offset = 0;

      real->segment_byte_offset = 0;
      real->segment_char_offset = 0;

      /* Find first segments in new line */
      real->any_segment = real->line->segments;
      real->segment = real->any_segment;
      while (real->segment->char_count == 0)
        real->segment = real->segment->next;

      return TRUE;
    }
  else
    {
      /* There is no way to move forward; we were already
         at the "end" index. (the end index is the last
         line pointer, segment_byte_offset of 0) */

      g_assert (real->line_char_offset == 0 ||
                real->line_byte_offset == 0);

      /* The only indexable segment allowed on the bogus
         line at the end is a single char segment containing
         a newline. */
      if (real->segments_changed_stamp ==
          gtk_text_btree_get_segments_changed_stamp (real->tree))
        {
          g_assert (real->segment->type == &gtk_text_char_type);
          g_assert (real->segment->char_count == 1);
        }
      /* We leave real->line as-is */

      return FALSE;
    }
}


/* The return value of this indicates WHETHER WE MOVED.
 * The return value of public functions indicates
 * (MOVEMENT OCCURRED && NEW ITER IS DEREFERENCEABLE)
 */
static gboolean
backward_line_leaving_caches_unmodified (GtkTextRealIter *real)
{
  GtkTextLine *new_line;

  new_line = gtk_text_line_previous (real->line);

  g_assert (new_line != real->line);

  if (new_line != NULL)
    {
      real->line = new_line;

      real->line_byte_offset = 0;
      real->line_char_offset = 0;

      real->segment_byte_offset = 0;
      real->segment_char_offset = 0;

      /* Find first segments in new line */
      real->any_segment = real->line->segments;
      real->segment = real->any_segment;
      while (real->segment->char_count == 0)
        real->segment = real->segment->next;

      return TRUE;
    }
  else
    {
      /* There is no way to move backward; we were already
         at the first line. */

      /* We leave real->line as-is */

      /* Note that we didn't clamp to the start of the first line. */

      return FALSE;
    }
}

/* The return value indicates (MOVEMENT OCCURRED && NEW ITER IS
 * DEREFERENCEABLE)
 */
static gboolean
forward_char (GtkTextRealIter *real)
{
  GtkTextIter *iter = (GtkTextIter*)real;

  check_invariants ((GtkTextIter*)real);

  ensure_char_offsets (real);

  if ( (real->segment_char_offset + 1) == real->segment->char_count)
    {
      /* Need to move to the next segment; if no next segment,
         need to move to next line. */
      return gtk_text_iter_forward_indexable_segment (iter);
    }
  else
    {
      /* Just moving within a segment. Keep byte count
         up-to-date, if it was already up-to-date. */

      g_assert (real->segment->type == &gtk_text_char_type);

      if (real->line_byte_offset >= 0)
        {
          gint bytes;
          const char * start =
            real->segment->body.chars + real->segment_byte_offset;

          bytes = g_utf8_next_char (start) - start;

          real->line_byte_offset += bytes;
          real->segment_byte_offset += bytes;

          g_assert (real->segment_byte_offset < real->segment->byte_count);
        }

      real->line_char_offset += 1;
      real->segment_char_offset += 1;

      adjust_char_index (real, 1);

      g_assert (real->segment_char_offset < real->segment->char_count);

      /* We moved into the middle of a segment, so the any_segment
         must now be the segment we're in the middle of. */
      real->any_segment = real->segment;

      check_invariants ((GtkTextIter*)real);

      if (gtk_text_iter_is_last ((GtkTextIter*)real))
        return FALSE;
      else
        return TRUE;
    }
}

gboolean
gtk_text_iter_forward_indexable_segment (GtkTextIter *iter)
{
  /* Need to move to the next segment; if no next segment,
     need to move to next line. */
  GtkTextLineSegment *seg;
  GtkTextLineSegment *any_seg;
  GtkTextRealIter *real;
  gint chars_skipped;
  gint bytes_skipped;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (real->line_char_offset >= 0)
    {
      chars_skipped = real->segment->char_count - real->segment_char_offset;
      g_assert (chars_skipped > 0);
    }
  else
    chars_skipped = 0;

  if (real->line_byte_offset >= 0)
    {
      bytes_skipped = real->segment->byte_count - real->segment_byte_offset;
      g_assert (bytes_skipped > 0);
    }
  else
    bytes_skipped = 0;

  /* Get first segment of any kind */
  any_seg = real->segment->next;
  /* skip non-indexable segments, if any */
  seg = any_seg;
  while (seg != NULL && seg->char_count == 0)
    seg = seg->next;

  if (seg != NULL)
    {
      real->any_segment = any_seg;
      real->segment = seg;

      if (real->line_byte_offset >= 0)
        {
          g_assert (bytes_skipped > 0);
          real->segment_byte_offset = 0;
          real->line_byte_offset += bytes_skipped;
        }

      if (real->line_char_offset >= 0)
        {
          g_assert (chars_skipped > 0);
          real->segment_char_offset = 0;
          real->line_char_offset += chars_skipped;
          adjust_char_index (real, chars_skipped);
        }

      check_invariants (iter);

      return TRUE;
    }
  else
    {
      /* End of the line */
      if (forward_line_leaving_caches_unmodified (real))
        {
          adjust_line_number (real, 1);
          if (real->line_char_offset >= 0)
            adjust_char_index (real, chars_skipped);

          g_assert (real->line_byte_offset == 0);
          g_assert (real->line_char_offset == 0);
          g_assert (real->segment_byte_offset == 0);
          g_assert (real->segment_char_offset == 0);
          g_assert (gtk_text_iter_starts_line (iter));

          check_invariants (iter);

          if (gtk_text_iter_is_last (iter))
            return FALSE;
          else
            return TRUE;
        }
      else
        {
          /* End of buffer */

          check_invariants (iter);

          return FALSE;
        }
    }
}

static gboolean
at_last_indexable_segment (GtkTextRealIter *real)
{
  GtkTextLineSegment *seg;

  /* Return TRUE if there are no indexable segments after
   * this iterator.
   */

  seg = real->segment->next;
  while (seg)
    {
      if (seg->char_count > 0)
        return FALSE;
      seg = seg->next;
    }
  return TRUE;
}

/* Goes back to the start of the next segment, even if
 * we're not at the start of the current segment (always
 * ends up on a different segment if it returns TRUE)
 */
gboolean
gtk_text_iter_backward_indexable_segment (GtkTextIter *iter)
{
  /* Move to the start of the previous segment; if no previous
   * segment, to the last segment in the previous line. This is
   * inherently a bit inefficient due to the singly-linked list and
   * tree nodes, but we can't afford the RAM for doubly-linked.
   */
  GtkTextRealIter *real;
  GtkTextLineSegment *seg;
  GtkTextLineSegment *any_seg;
  GtkTextLineSegment *prev_seg;
  GtkTextLineSegment *prev_any_seg;
  gint bytes_skipped;
  gint chars_skipped;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  /* Find first segments in line */
  any_seg = real->line->segments;
  seg = any_seg;
  while (seg->char_count == 0)
    seg = seg->next;

  if (seg == real->segment)
    {
      /* Could probably do this case faster by hand-coding the
       * iteration.
       */

      /* We were already at the start of a line;
       * go back to the previous line.
       */
      if (gtk_text_iter_backward_line (iter))
        {
          /* Go forward to last indexable segment in line. */
          while (!at_last_indexable_segment (real))
            gtk_text_iter_forward_indexable_segment (iter);

          check_invariants (iter);

          return TRUE;
        }
      else
        return FALSE; /* We were at the start of the first line. */
    }

  /* We must be in the middle of a line; so find the indexable
   * segment just before our current segment.
   */
  g_assert (seg != real->segment);
  while (seg != real->segment)
    {
      prev_seg = seg;
      prev_any_seg = any_seg;

      any_seg = seg->next;
      seg = any_seg;
      while (seg->char_count == 0)
        seg = seg->next;
    }

  g_assert (prev_seg != NULL);
  g_assert (prev_any_seg != NULL);
  g_assert (prev_seg->char_count > 0);

  /* We skipped the entire previous segment, plus any
   * chars we were into the current segment.
   */
  if (real->segment_byte_offset >= 0)
    bytes_skipped = prev_seg->byte_count + real->segment_byte_offset;
  else
    bytes_skipped = -1;

  if (real->segment_char_offset >= 0)
    chars_skipped = prev_seg->char_count + real->segment_char_offset;
  else
    chars_skipped = -1;

  real->segment = prev_seg;
  real->any_segment = prev_any_seg;
  real->segment_byte_offset = 0;
  real->segment_char_offset = 0;

  if (bytes_skipped >= 0)
    {
      if (real->line_byte_offset >= 0)
        {
          real->line_byte_offset -= bytes_skipped;
          g_assert (real->line_byte_offset >= 0);
        }
    }
  else
    real->line_byte_offset = -1;

  if (chars_skipped >= 0)
    {
      if (real->line_char_offset >= 0)
        {
          real->line_char_offset -= chars_skipped;
          g_assert (real->line_char_offset >= 0);
        }

      if (real->cached_char_index >= 0)
        {
          real->cached_char_index -= chars_skipped;
          g_assert (real->cached_char_index >= 0);
        }
    }
  else
    {
      real->line_char_offset = -1;
      real->cached_char_index = -1;
    }

  /* line number is unchanged. */

  check_invariants (iter);

  return TRUE;
}

/**
 * gtk_text_iter_next_char:
 * @iter: an iterator
 *
 * Moves @iter forward by one character offset. Note that images
 * embedded in the buffer occupy 1 character slot, so
 * gtk_text_iter_next_char () may actually move onto an image instead
 * of a character, if you have images in your buffer.  If @iter is the
 * end iterator or one character before it, @iter will now point at
 * the end iterator, and gtk_text_iter_next_char () returns FALSE for
 * convenience when writing loops.
 *
 * Return value: whether the new position is the end iterator
 **/
gboolean
gtk_text_iter_next_char (GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else
    {
      check_invariants (iter);
      return forward_char (real);
    }
}

/**
 * gtk_text_iter_prev_char:
 * @iter: an iterator
 *
 * Moves backward by one character offset. Returns TRUE if movement
 * was possible; if @iter was the first in the buffer (character
 * offset 0), gtk_text_iter_prev_char () returns FALSE for convenience when
 * writing loops.
 *
 * Return value: whether movement was possible
 **/
gboolean
gtk_text_iter_prev_char (GtkTextIter *iter)
{
  g_return_val_if_fail (iter != NULL, FALSE);

  check_invariants (iter);

  return gtk_text_iter_backward_chars (iter, 1);
}

/*
  Definitely we should try to linear scan as often as possible for
  movement within a single line, because we can't use the BTree to
  speed within-line searches up; for movement between lines, we would
  like to avoid the linear scan probably.

  Instead of using this constant, it might be nice to cache the line
  length in the iterator and linear scan if motion is within a single
  line.

  I guess you'd have to profile the various approaches.
*/
#define MAX_LINEAR_SCAN 150


/**
 * gtk_text_iter_forward_chars:
 * @iter: an iterator
 * @count: number of characters to move, may be negative
 *
 * Moves @count characters if possible (if @count would move past the
 * start or end of the buffer, moves to the start or end of the
 * buffer). The return value indicates whether the new position of
 * @iter is different from its original position, and dereferenceable
 * (the last iterator in the buffer is not dereferenceable). If @count
 * is 0, the function does nothing and returns FALSE.
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_forward_chars (GtkTextIter *iter, gint count)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else if (count == 0)
    return FALSE;
  else if (count < 0)
    return gtk_text_iter_backward_chars (iter, 0 - count);
  else if (count < MAX_LINEAR_SCAN)
    {
      check_invariants (iter);

      while (count > 1)
        {
          if (!forward_char (real))
            return FALSE;
          --count;
        }

      return forward_char (real);
    }
  else
    {
      gint current_char_index;
      gint new_char_index;

      check_invariants (iter);

      current_char_index = gtk_text_iter_get_offset (iter);

      if (current_char_index == gtk_text_btree_char_count (real->tree))
        return FALSE; /* can't move forward */

      new_char_index = current_char_index + count;
      gtk_text_iter_set_offset (iter, new_char_index);

      check_invariants (iter);

      /* Return FALSE if we're on the non-dereferenceable end
       * iterator.
       */
      if (gtk_text_iter_is_last (iter))
        return FALSE;
      else
        return TRUE;
    }
}

/**
 * gtk_text_iter_backward_chars:
 * @iter: an iterator
 * @count: number of characters to move
 *
 * Moves @count characters backward, if possible (if @count would move
 * past the start or end of the buffer, moves to the start or end of
 * the buffer).  The return value indicates whether the iterator moved
 * onto a dereferenceable position; if the iterator didn't move, or
 * moved onto the end iterator, then FALSE is returned. If @count is 0,
 * the function does nothing and returns FALSE.
 *
 * Return value: whether @iter moved and is dereferenceable
 *
 **/
gboolean
gtk_text_iter_backward_chars (GtkTextIter *iter, gint count)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;
  else if (count == 0)
    return FALSE;
  else if (count < 0)
    return gtk_text_iter_forward_chars (iter, 0 - count);

  ensure_char_offsets (real);
  check_invariants (iter);

  if (count <= real->segment_char_offset)
    {
      /* Optimize the within-segment case */
      g_assert (real->segment->char_count > 0);
      g_assert (real->segment->type == &gtk_text_char_type);

      real->segment_char_offset -= count;
      g_assert (real->segment_char_offset >= 0);

      if (real->line_byte_offset >= 0)
        {
          gint new_byte_offset;
          gint i;

          new_byte_offset = 0;
          i = 0;
          while (i < real->segment_char_offset)
            {
              const char * start = real->segment->body.chars + new_byte_offset;
              new_byte_offset += g_utf8_next_char (start) - start;

              ++i;
            }

          real->line_byte_offset -= (real->segment_byte_offset - new_byte_offset);
          real->segment_byte_offset = new_byte_offset;
        }

      real->line_char_offset -= count;

      adjust_char_index (real, 0 - count);

      check_invariants (iter);

      return TRUE;
    }
  else
    {
      /* We need to go back into previous segments. For now,
       * just keep this really simple. FIXME
       * use backward_indexable_segment.
       */
      if (TRUE || count > MAX_LINEAR_SCAN)
        {
          gint current_char_index;
          gint new_char_index;

          current_char_index = gtk_text_iter_get_offset (iter);

          if (current_char_index == 0)
            return FALSE; /* can't move backward */

          new_char_index = current_char_index - count;
          if (new_char_index < 0)
            new_char_index = 0;
          gtk_text_iter_set_offset (iter, new_char_index);

          check_invariants (iter);

          return TRUE;
        }
      else
        {
          /* FIXME backward_indexable_segment here */

          return FALSE;
        }
    }
}

#if 0

/* These two can't be implemented efficiently (always have to use
 * a linear scan, since that's the only way to find all the non-text
 * segments)
 */

/**
 * gtk_text_iter_forward_text_chars:
 * @iter: a #GtkTextIter
 * @count: number of chars to move
 *
 * Moves forward by @count text characters (pixbufs, widgets,
 * etc. do not count as characters for this). Equivalent to moving
 * through the results of gtk_text_iter_get_text (), rather than
 * gtk_text_iter_get_slice ().
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_forward_text_chars  (GtkTextIter *iter,
                                   gint         count)
{



}

/**
 * gtk_text_iter_forward_text_chars:
 * @iter: a #GtkTextIter
 * @count: number of chars to move
 *
 * Moves backward by @count text characters (pixbufs, widgets,
 * etc. do not count as characters for this). Equivalent to moving
 * through the results of gtk_text_iter_get_text (), rather than
 * gtk_text_iter_get_slice ().
 *
 * Return value: whether @iter moved and is dereferenceable
 **/
gboolean
gtk_text_iter_backward_text_chars (GtkTextIter *iter,
                                   gint         count)
{


}
#endif

/**
 * gtk_text_iter_forward_line:
 * @iter: an iterator
 *
 * Moves @iter to the start of the next line. Returns TRUE if there
 * was a next line to move to, and FALSE if @iter was simply moved to
 * the end of the buffer and is now not dereferenceable, or if @iter was
 * already at the end of the buffer.
 *
 * Return value: whether @iter can be dereferenced
 **/
gboolean
gtk_text_iter_forward_line (GtkTextIter *iter)
{
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  if (forward_line_leaving_caches_unmodified (real))
    {
      invalidate_char_index (real);
      adjust_line_number (real, 1);

      check_invariants (iter);

      if (gtk_text_iter_is_last (iter))
        return FALSE;
      else
        return TRUE;
    }
  else
    {
      check_invariants (iter);
      return FALSE;
    }
}

/**
 * gtk_text_iter_backward_line:
 * @iter: an iterator
 *
 * Moves @iter to the start of the previous line. Returns TRUE if
 * @iter could be moved; i.e. if @iter was at character offset 0, this
 * function returns FALSE. Therefore if @iter was already on line 0,
 * but not at the start of the line, @iter is snapped to the start of
 * the line and the function returns TRUE. (Note that this implies that
 * in a loop calling this function, the line number may not change on
 * every iteration, if your first iteration is on line 0.)
 *
 * Return value: whether @iter moved
 **/
gboolean
gtk_text_iter_backward_line (GtkTextIter *iter)
{
  GtkTextLine *new_line;
  GtkTextRealIter *real;
  gboolean offset_will_change;
  gint offset;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  new_line = gtk_text_line_previous (real->line);

  offset_will_change = FALSE;
  if (real->line_char_offset > 0)
    offset_will_change = TRUE;

  if (new_line != NULL)
    {
      real->line = new_line;

      adjust_line_number (real, -1);
    }
  else
    {
      if (!offset_will_change)
        return FALSE;
    }

  invalidate_char_index (real);

  real->line_byte_offset = 0;
  real->line_char_offset = 0;

  real->segment_byte_offset = 0;
  real->segment_char_offset = 0;

  /* Find first segment in line */
  real->any_segment = real->line->segments;
  real->segment = gtk_text_line_byte_to_segment (real->line,
                                                 0, &offset);

  g_assert (offset == 0);

  /* Note that if we are on the first line, we snap to the start of
   * the first line and return TRUE, so TRUE means the iterator
   * changed, not that the line changed; this is maybe a bit
   * weird. I'm not sure there's an obvious right thing to do though.
   */

  check_invariants (iter);

  return TRUE;
}

gboolean
gtk_text_iter_forward_lines (GtkTextIter *iter, gint count)
{
  if (count < 0)
    return gtk_text_iter_backward_lines (iter, 0 - count);
  else if (count == 0)
    return FALSE;
  else if (count == 1)
    {
      check_invariants (iter);
      return gtk_text_iter_forward_line (iter);
    }
  else
    {
      gint old_line;

      old_line = gtk_text_iter_get_line (iter);

      gtk_text_iter_set_line (iter, old_line + count);

      check_invariants (iter);

      /* return whether it moved, and is dereferenceable. */
      return
        (gtk_text_iter_get_line (iter) != old_line) &&
        !gtk_text_iter_is_last (iter);
    }
}

gboolean
gtk_text_iter_backward_lines (GtkTextIter *iter, gint count)
{
  if (count < 0)
    return gtk_text_iter_forward_lines (iter, 0 - count);
  else if (count == 0)
    return FALSE;
  else if (count == 1)
    {
      return gtk_text_iter_backward_line (iter);
    }
  else
    {
      gint old_line;

      old_line = gtk_text_iter_get_line (iter);

      gtk_text_iter_set_line (iter, MAX (old_line - count, 0));

      return (gtk_text_iter_get_line (iter) != old_line);
    }
}

typedef gboolean (* FindLogAttrFunc) (PangoLogAttr *attrs,
                                      gint          offset,
                                      gint          min_offset,
                                      gint          len,
                                      gint         *found_offset);

static gboolean
find_word_end_func (PangoLogAttr *attrs,
                    gint          offset,
                    gint          min_offset,
                    gint          len,
                    gint         *found_offset)
{
  ++offset; /* We always go to the NEXT word end */

  /* Find start of next word */
  while (offset < min_offset + len &&
         !attrs[offset].is_word_stop)
    ++offset;

  /* Find end */
  while (offset < min_offset + len &&
         !attrs[offset].is_white)
    ++offset;

  *found_offset = offset;

  return offset < min_offset + len;
}

static gboolean
find_word_start_func (PangoLogAttr *attrs,
                      gint          offset,
                      gint          min_offset,
                      gint          len,
                      gint         *found_offset)
{
  --offset; /* We always go to the NEXT word start */

  /* Find end of prev word */
  while (offset >= min_offset &&
         attrs[offset].is_white)
    --offset;

  /* Find start */
  while (offset >= min_offset &&
         !attrs[offset].is_word_stop)
    --offset;

  *found_offset = offset;

  return offset >= min_offset;
}

/* FIXME this function is very, very gratuitously slow */
static gboolean
find_by_log_attrs (GtkTextIter *iter,
                   FindLogAttrFunc func,
                   gboolean forward)
{
  GtkTextIter orig;
  GtkTextIter start;
  GtkTextIter end;
  gchar *paragraph;
  gint char_len, byte_len;
  PangoLogAttr *attrs;
  int offset;
  gboolean found = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);

  orig = *iter;
  start = *iter;
  end = *iter;

  gtk_text_iter_set_line_offset (&start, 0);
  gtk_text_iter_forward_to_newline (&end);

  paragraph = gtk_text_iter_get_text (&start, &end);
  char_len = g_utf8_strlen (paragraph, -1);
  byte_len = strlen (paragraph);

  offset = gtk_text_iter_get_line_offset (iter);

  if (char_len > 0 && offset < char_len)
    {
      gchar *lang;

      attrs = g_new (PangoLogAttr, char_len);

      lang = gtk_text_iter_get_language (iter);

      pango_get_log_attrs (paragraph, byte_len, -1,
                           lang,
                           attrs);

      g_free (lang);

      found = (* func) (attrs, offset, 0, char_len, &offset);

      g_free (attrs);
    }

  g_free (paragraph);

  if (!found)
    {
      if (forward)
        {
          if (gtk_text_iter_forward_line (iter))
            return find_by_log_attrs (iter, func, forward);
          else
            return FALSE;
        }
      else
        {
          if (gtk_text_iter_backward_line (iter))
            return find_by_log_attrs (iter, func, forward);
          else
            return FALSE;
        }
    }
  else
    {
      gtk_text_iter_set_line_offset (iter, offset);

      return
        !gtk_text_iter_equal (iter, &orig) &&
        !gtk_text_iter_is_last (iter);
    }
}

gboolean
gtk_text_iter_forward_word_end (GtkTextIter *iter)
{
  return find_by_log_attrs (iter, find_word_end_func, TRUE);
}

gboolean
gtk_text_iter_backward_word_start (GtkTextIter      *iter)
{
  return find_by_log_attrs (iter, find_word_start_func, FALSE);
}

/* FIXME a loop around a truly slow function means
 * a truly spectacularly slow function.
 */
gboolean
gtk_text_iter_forward_word_ends (GtkTextIter      *iter,
                                 gint               count)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (count > 0, FALSE);

  if (!gtk_text_iter_forward_word_end (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_forward_word_end (iter))
        break;
      --count;
    }
  return TRUE;
}

gboolean
gtk_text_iter_backward_word_starts (GtkTextIter      *iter,
                                    gint               count)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (count > 0, FALSE);

  if (!gtk_text_iter_backward_word_start (iter))
    return FALSE;
  --count;

  while (count > 0)
    {
      if (!gtk_text_iter_backward_word_start (iter))
        break;
      --count;
    }
  return TRUE;
}

void
gtk_text_iter_set_line_offset (GtkTextIter *iter,
                               gint char_on_line)
{
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  iter_set_from_char_offset (real, real->line, char_on_line);

  check_invariants (iter);
}

void
gtk_text_iter_set_line_index (GtkTextIter *iter,
                              gint         byte_on_line)
{
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  iter_set_from_byte_offset (real, real->line, byte_on_line);

  if (real->segment->type == &gtk_text_char_type &&
      (real->segment->body.chars[real->segment_byte_offset] & 0xc0) == 0x80)
    g_warning ("%s: Incorrect byte offset %d falls in the middle of a UTF-8 "
               "character; this will crash the text buffer. "
               "Byte indexes must refer to the start of a character.",
               G_STRLOC, byte_on_line);

  check_invariants (iter);
}

void
gtk_text_iter_set_line (GtkTextIter *iter,
                        gint         line_number)
{
  GtkTextLine *line;
  gint real_line;
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  line = gtk_text_btree_get_line (real->tree, line_number, &real_line);

  iter_set_from_char_offset (real, line, 0);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  check_invariants (iter);
}

void
gtk_text_iter_set_offset (GtkTextIter *iter, gint char_index)
{
  GtkTextLine *line;
  GtkTextRealIter *real;
  gint line_start;
  gint real_char_index;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  check_invariants (iter);

  if (real->cached_char_index >= 0 &&
      real->cached_char_index == char_index)
    return;

  line = gtk_text_btree_get_line_at_char (real->tree,
                                          char_index,
                                          &line_start,
                                          &real_char_index);

  iter_set_from_char_offset (real, line, real_char_index - line_start);

  /* Go ahead and cache this since we have it. */
  real->cached_char_index = real_char_index;

  check_invariants (iter);
}

void
gtk_text_iter_forward_to_end  (GtkTextIter       *iter)
{
  GtkTextBuffer *buffer;
  GtkTextRealIter *real;

  g_return_if_fail (iter != NULL);

  real = gtk_text_iter_make_surreal (iter);

  if (real == NULL)
    return;

  buffer = gtk_text_btree_get_buffer (real->tree);

  gtk_text_buffer_get_last_iter (buffer, iter);
}

gboolean
gtk_text_iter_forward_to_newline (GtkTextIter *iter)
{
  gint current_offset;
  gint new_offset;

  g_return_val_if_fail (iter != NULL, FALSE);

  current_offset = gtk_text_iter_get_line_offset (iter);
  new_offset = gtk_text_iter_get_chars_in_line (iter) - 1;

  if (current_offset < new_offset)
    {
      /* Move to end of this line. */
      gtk_text_iter_set_line_offset (iter, new_offset);
      return TRUE;
    }
  else
    {
      /* Move to end of next line. */
      if (gtk_text_iter_forward_line (iter))
        {
          /* We don't want to move past all
           * empty lines.
           */
          if (gtk_text_iter_get_char (iter) != '\n')
            gtk_text_iter_forward_to_newline (iter);
          return TRUE;
        }
      else
        return FALSE;
    }
}

/**
 * gtk_text_iter_forward_to_tag_toggle:
 * @iter: a #GtkTextIter
 * @tag: a #GtkTextTag, or NULL
 *
 * Moves forward to the next toggle (on or off) of the
 * #GtkTextTag @tag, or to the next toggle of any tag if
 * @tag is NULL. If no matching tag toggles are found,
 * returns FALSE, otherwise TRUE. Does not return toggles
 * located at @iter, only toggles after @iter. Sets @iter to
 * the location of the toggle, or to the end of the buffer
 * if no toggle is found.
 *
 * Return value: whether we found a tag toggle after @iter
 **/
gboolean
gtk_text_iter_forward_to_tag_toggle (GtkTextIter *iter,
                                     GtkTextTag  *tag)
{
  GtkTextLine *next_line;
  GtkTextLine *current_line;
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  current_line = real->line;
  next_line = gtk_text_line_next_could_contain_tag (current_line,
                                                    real->tree, tag);

  while (gtk_text_iter_forward_indexable_segment (iter))
    {
      /* If we went forward to a line that couldn't contain a toggle
         for the tag, then skip forward to a line that could contain
         it. This potentially skips huge hunks of the tree, so we
         aren't a purely linear search. */
      if (real->line != current_line)
        {
          if (next_line == NULL)
            {
              /* End of search. Set to end of buffer. */
              gtk_text_btree_get_last_iter (real->tree, iter);
              return FALSE;
            }

          if (real->line != next_line)
            iter_set_from_byte_offset (real, next_line, 0);

          current_line = real->line;
          next_line = gtk_text_line_next_could_contain_tag (current_line,
                                                            real->tree,
                                                            tag);
        }

      if (gtk_text_iter_toggles_tag (iter, tag))
        {
          /* If there's a toggle here, it isn't indexable so
             any_segment can't be the indexable segment. */
          g_assert (real->any_segment != real->segment);
          return TRUE;
        }
    }

  /* Check end iterator for tags */
  if (gtk_text_iter_toggles_tag (iter, tag))
    {
      /* If there's a toggle here, it isn't indexable so
         any_segment can't be the indexable segment. */
      g_assert (real->any_segment != real->segment);
      return TRUE;
    }

  /* Reached end of buffer */
  return FALSE;
}

/**
 * gtk_text_iter_backward_to_tag_toggle:
 * @iter: a #GtkTextIter
 * @tag: a #GtkTextTag, or NULL
 *
 * Moves backward to the next toggle (on or off) of the
 * #GtkTextTag @tag, or to the next toggle of any tag if
 * @tag is NULL. If no matching tag toggles are found,
 * returns FALSE, otherwise TRUE. Does not return toggles
 * located at @iter, only toggles before @iter. Sets @iter
 * to the location of the toggle, or the start of the buffer
 * if no toggle is found.
 *
 * Return value: whether we found a tag toggle before @iter
 **/
gboolean
gtk_text_iter_backward_to_tag_toggle (GtkTextIter *iter,
                                      GtkTextTag  *tag)
{
  GtkTextLine *prev_line;
  GtkTextLine *current_line;
  GtkTextRealIter *real;

  g_return_val_if_fail (iter != NULL, FALSE);

  real = gtk_text_iter_make_real (iter);

  if (real == NULL)
    return FALSE;

  check_invariants (iter);

  current_line = real->line;
  prev_line = gtk_text_line_previous_could_contain_tag (current_line,
                                                        real->tree, tag);


  /* If we're at segment start, go to the previous segment;
   * if mid-segment, snap to start of current segment.
   */
  if (is_segment_start (real))
    {
      if (!gtk_text_iter_backward_indexable_segment (iter))
        return FALSE;
    }
  else
    {
      ensure_char_offsets (real);

      if (!gtk_text_iter_backward_chars (iter, real->segment_char_offset))
        return FALSE;
    }

  do
    {
      /* If we went backward to a line that couldn't contain a toggle
       * for the tag, then skip backward further to a line that
       * could contain it. This potentially skips huge hunks of the
       * tree, so we aren't a purely linear search.
       */
      if (real->line != current_line)
        {
          if (prev_line == NULL)
            {
              /* End of search. Set to start of buffer. */
              gtk_text_btree_get_iter_at_char (real->tree, iter, 0);
              return FALSE;
            }

          if (real->line != prev_line)
            {
              /* Set to last segment in prev_line (could do this
               * more quickly)
               */
              iter_set_from_byte_offset (real, prev_line, 0);

              while (!at_last_indexable_segment (real))
                gtk_text_iter_forward_indexable_segment (iter);
            }

          current_line = real->line;
          prev_line = gtk_text_line_previous_could_contain_tag (current_line,
                                                                real->tree,
                                                                tag);
        }

      if (gtk_text_iter_toggles_tag (iter, tag))
        {
          /* If there's a toggle here, it isn't indexable so
           * any_segment can't be the indexable segment.
           */
          g_assert (real->any_segment != real->segment);
          return TRUE;
        }
    }
  while (gtk_text_iter_backward_indexable_segment (iter));

  /* Reached front of buffer */
  return FALSE;
}

static gboolean
matches_pred (GtkTextIter *iter,
              GtkTextCharPredicate pred,
              gpointer user_data)
{
  gint ch;

  ch = gtk_text_iter_get_char (iter);

  return (*pred) (ch, user_data);
}

/**
 * gtk_text_iter_forward_find_char:
 * @iter: a #GtkTextIter
 * @pred: a function to be called on each character
 * @user_data: user data for @pred
 * @limit: search limit, or %NULL for none 
 * 
 * Advances @iter, calling @pred on each character. If
 * @pred returns %TRUE, returns %TRUE and stops scanning.
 * If @pred never returns %TRUE, @iter is set to @limit if
 * @limit is non-%NULL, otherwise to the end iterator.
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_forward_find_char (GtkTextIter         *iter,
                                 GtkTextCharPredicate pred,
                                 gpointer             user_data,
                                 const GtkTextIter   *limit)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (pred != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) >= 0)
    return FALSE;
  
  while ((limit == NULL ||
          !gtk_text_iter_equal (limit, iter)) &&
         gtk_text_iter_next_char (iter))
    {      
      if (matches_pred (iter, pred, user_data))
        return TRUE;
    }

  return FALSE;
}

gboolean
gtk_text_iter_backward_find_char (GtkTextIter         *iter,
                                  GtkTextCharPredicate pred,
                                  gpointer             user_data,
                                  const GtkTextIter   *limit)
{
  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (pred != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) <= 0)
    return FALSE;
  
  while ((limit == NULL ||
          !gtk_text_iter_equal (limit, iter)) &&
         gtk_text_iter_prev_char (iter))
    {
      if (matches_pred (iter, pred, user_data))
        return TRUE;
    }

  return FALSE;
}

static void
forward_chars_with_skipping (GtkTextIter *iter,
                             gint         count,
                             gboolean     skip_invisible,
                             gboolean     skip_nontext)
{

  gint i;

  g_return_if_fail (count >= 0);

  i = count;

  while (i > 0)
    {
      gboolean ignored = FALSE;

      if (skip_nontext &&
          gtk_text_iter_get_char (iter) == gtk_text_unknown_char)
        ignored = TRUE;

      if (!ignored &&
          skip_invisible &&
          gtk_text_btree_char_is_invisible (iter))
        ignored = TRUE;

      gtk_text_iter_next_char (iter);

      if (!ignored)
        --i;
    }
}

static gboolean
lines_match (const GtkTextIter *start,
             const gchar **lines,
             gboolean visible_only,
             gboolean slice,
             GtkTextIter *match_start,
             GtkTextIter *match_end)
{
  GtkTextIter next;
  gchar *line_text;
  const gchar *found;
  gint offset;

  if (*lines == NULL || **lines == '\0')
    {
      if (match_start)
        *match_start = *start;

      if (match_end)
        *match_end = *start;
      return TRUE;
    }

  next = *start;
  gtk_text_iter_forward_line (&next);

  /* No more text in buffer, but *lines is nonempty */
  if (gtk_text_iter_equal (start, &next))
    {
      return FALSE;
    }

  if (slice)
    {
      if (visible_only)
        line_text = gtk_text_iter_get_visible_slice (start, &next);
      else
        line_text = gtk_text_iter_get_slice (start, &next);
    }
  else
    {
      if (visible_only)
        line_text = gtk_text_iter_get_visible_text (start, &next);
      else
        line_text = gtk_text_iter_get_text (start, &next);
    }

  if (match_start) /* if this is the first line we're matching */
    found = strstr (line_text, *lines);
  else
    {
      /* If it's not the first line, we have to match from the
       * start of the line.
       */
      if (strncmp (line_text, *lines, strlen (*lines)) == 0)
        found = line_text;
      else
        found = NULL;
    }

  if (found == NULL)
    {
      g_free (line_text);
      return FALSE;
    }

  /* Get offset to start of search string */
  offset = g_utf8_strlen (line_text, found - line_text);

  next = *start;

  /* If match start needs to be returned, set it to the
   * start of the search string.
   */
  if (match_start)
    {
      *match_start = next;

      forward_chars_with_skipping (match_start, offset,
                                   visible_only, !slice);
    }

  /* Go to end of search string */
  offset += g_utf8_strlen (*lines, -1);

  forward_chars_with_skipping (&next, offset,
                               visible_only, !slice);

  g_free (line_text);

  ++lines;

  if (match_end)
    *match_end = next;

  /* pass NULL for match_start, since we don't need to find the
   * start again.
   */
  return lines_match (&next, lines, visible_only, slice, NULL, match_end);
}

/* strsplit () that retains the delimiter as part of the string. */
static gchar **
strbreakup (const char *string,
            const char *delimiter,
            gint        max_tokens)
{
  GSList *string_list = NULL, *slist;
  gchar **str_array, *s;
  guint i, n = 1;

  g_return_val_if_fail (string != NULL, NULL);
  g_return_val_if_fail (delimiter != NULL, NULL);

  if (max_tokens < 1)
    max_tokens = G_MAXINT;

  s = strstr (string, delimiter);
  if (s)
    {
      guint delimiter_len = strlen (delimiter);

      do
        {
          guint len;
          gchar *new_string;

          len = s - string + delimiter_len;
          new_string = g_new (gchar, len + 1);
          strncpy (new_string, string, len);
          new_string[len] = 0;
          string_list = g_slist_prepend (string_list, new_string);
          n++;
          string = s + delimiter_len;
          s = strstr (string, delimiter);
        }
      while (--max_tokens && s);
    }
  if (*string)
    {
      n++;
      string_list = g_slist_prepend (string_list, g_strdup (string));
    }

  str_array = g_new (gchar*, n);

  i = n - 1;

  str_array[i--] = NULL;
  for (slist = string_list; slist; slist = slist->next)
    str_array[i--] = slist->data;

  g_slist_free (string_list);

  return str_array;
}

/**
 * gtk_text_iter_forward_search:
 * @iter: start of search
 * @str: a search string
 * @visible_only: if %TRUE, search only visible text
 * @slice: if %TRUE, @str contains 0xFFFD when we want to match widgets, pixbufs
 * @match_start: return location for start of match, or %NULL
 * @match_end: return location for end of match, or %NULL
 * @limit: bound for the search, or %NULL for the end of the buffer
 * 
 * 
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_forward_search (const GtkTextIter *iter,
                              const gchar       *str,
                              gboolean           visible_only,
                              gboolean           slice,
                              GtkTextIter       *match_start,
                              GtkTextIter       *match_end,
                              const GtkTextIter *limit)
{
  gchar **lines = NULL;
  GtkTextIter match;
  gboolean retval = FALSE;
  GtkTextIter search;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (str != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (iter, limit) >= 0)
    return FALSE;
  
  if (*str == '\0')
    {
      /* If we can move one char, return the empty string there */
      match = *iter;
      
      if (gtk_text_iter_next_char (&match))
        {
          if (limit &&
              gtk_text_iter_equal (&match, limit))
            return FALSE;
          
          if (match_start)
            *match_start = match;
          if (match_end)
            *match_end = match;
          return TRUE;
        }
      else
        return FALSE;
    }

  /* locate all lines */

  lines = strbreakup (str, "\n", -1);

  search = *iter;

  do
    {
      /* This loop has an inefficient worst-case, where
       * gtk_text_iter_get_text () is called repeatedly on
       * a single line.
       */
      GtkTextIter end;

      if (limit &&
          gtk_text_iter_compare (&search, limit) >= 0)
        break;
      
      if (lines_match (&search, (const gchar**)lines,
                       visible_only, slice, &match, &end))
        {
          if (limit == NULL ||
              (limit &&
               gtk_text_iter_compare (&end, limit) < 0))
            {
              retval = TRUE;
              
              if (match_start)
                *match_start = match;
              
              if (match_end)
                *match_end = end;
            }
          
          break;
        }
    }
  while (gtk_text_iter_forward_line (&search));

  g_strfreev ((gchar**)lines);

  return retval;
}

static gboolean
vectors_equal_ignoring_trailing (gchar **vec1,
                                 gchar **vec2)
{
  /* Ignores trailing chars in vec2's last line */

  gchar **i1, **i2;

  i1 = vec1;
  i2 = vec2;

  while (*i1 && *i2)
    {
      if (strcmp (*i1, *i2) != 0)
        {
          if (*(i2 + 1) == NULL) /* if this is the last line */
            {
              gint len1 = strlen (*i1);
              gint len2 = strlen (*i2);

              if (len2 >= len1 &&
                  strncmp (*i1, *i2, len1) == 0)
                {
                  /* We matched ignoring the trailing stuff in vec2 */
                  return TRUE;
                }
              else
                {
                  return FALSE;
                }
            }
          else
            {
              return FALSE;
            }
        }
      ++i1;
      ++i2;
    }

  if (*i1 || *i2)
    {
      return FALSE;
    }
  else
    return TRUE;
}

typedef struct _LinesWindow LinesWindow;

struct _LinesWindow
{
  gint n_lines;
  gchar **lines;
  GtkTextIter first_line_start;
  GtkTextIter first_line_end;
  gboolean slice;
  gboolean visible_only;
};

static void
lines_window_init (LinesWindow       *win,
                   const GtkTextIter *start)
{
  gint i;
  GtkTextIter line_start;
  GtkTextIter line_end;

  /* If we start on line 1, there are 2 lines to search (0 and 1), so
   * n_lines can be 2.
   */
  if (gtk_text_iter_is_first (start) ||
      gtk_text_iter_get_line (start) + 1 < win->n_lines)
    {
      /* Already at the end, or not enough lines to match */
      win->lines = g_new0 (gchar*, 1);
      *win->lines = NULL;
      return;
    }

  line_start = *start;
  line_end = *start;

  /* Move to start iter to start of line */
  gtk_text_iter_set_line_offset (&line_start, 0);

  if (gtk_text_iter_equal (&line_start, &line_end))
    {
      /* we were already at the start; so go back one line */
      gtk_text_iter_backward_line (&line_start);
    }

  win->first_line_start = line_start;
  win->first_line_end = line_end;

  win->lines = g_new0 (gchar*, win->n_lines + 1);

  i = win->n_lines - 1;
  while (i >= 0)
    {
      gchar *line_text;

      if (win->slice)
        {
          if (win->visible_only)
            line_text = gtk_text_iter_get_visible_slice (&line_start, &line_end);
          else
            line_text = gtk_text_iter_get_slice (&line_start, &line_end);
        }
      else
        {
          if (win->visible_only)
            line_text = gtk_text_iter_get_visible_text (&line_start, &line_end);
          else
            line_text = gtk_text_iter_get_text (&line_start, &line_end);
        }

      win->lines[i] = line_text;

      line_end = line_start;
      gtk_text_iter_backward_line (&line_start);

      --i;
    }
}

static gboolean
lines_window_back (LinesWindow *win)
{
  GtkTextIter new_start;
  gchar *line_text;

  new_start = win->first_line_start;

  if (!gtk_text_iter_backward_line (&new_start))
    return FALSE;
  else
    {
      win->first_line_start = new_start;
      win->first_line_end = new_start;

      gtk_text_iter_forward_line (&win->first_line_end);
    }

  if (win->slice)
    {
      if (win->visible_only)
        line_text = gtk_text_iter_get_visible_slice (&win->first_line_start,
                                                     &win->first_line_end);
      else
        line_text = gtk_text_iter_get_slice (&win->first_line_start,
                                             &win->first_line_end);
    }
  else
    {
      if (win->visible_only)
        line_text = gtk_text_iter_get_visible_text (&win->first_line_start,
                                                    &win->first_line_end);
      else
        line_text = gtk_text_iter_get_text (&win->first_line_start,
                                            &win->first_line_end);
    }

  /* Move lines to make room for first line. */
  g_memmove (win->lines + 1, win->lines, win->n_lines * sizeof (gchar*));

  *win->lines = line_text;

  /* Free old last line and NULL-terminate */
  g_free (win->lines[win->n_lines]);
  win->lines[win->n_lines] = NULL;

  return TRUE;
}

static void
lines_window_free (LinesWindow *win)
{
  g_strfreev (win->lines);
}

static gchar*
my_strrstr (const gchar *haystack,
            const gchar *needle)
{
  /* FIXME GLib should have a nice implementation in it, this
   * is slow-ass crap.
   */

  gint haystack_len = strlen (haystack);
  gint needle_len = strlen (needle);
  const gchar *needle_end = needle + needle_len;
  const gchar *haystack_rend = haystack - 1;
  const gchar *needle_rend = needle - 1;
  const gchar *p;

  p = haystack + haystack_len;
  while (p != haystack)
    {
      const gchar *n = needle_end - 1;
      const gchar *s = p - 1;
      while (s != haystack_rend &&
             n != needle_rend &&
             *s == *n)
        {
          --n;
          --s;
        }

      if (n == needle_rend)
        return (gchar*)++s;

      --p;
    }

  return NULL;
}

/**
 * gtk_text_iter_backward_search:
 * @iter: a #GtkTextIter where the search begins
 * @str: search string
 * @visible_only: if %TRUE search only visible text
 * @slice: if %TRUE the search string contains 0xFFFD to match pixbufs, widgets
 * @match_start: return location for start of match, or %NULL
 * @match_end: return location for end of match, or %NULL
 * @limit: location of last possible @match_start, or %NULL for start of buffer
 * 
 * 
 * 
 * Return value: whether a match was found
 **/
gboolean
gtk_text_iter_backward_search (const GtkTextIter *iter,
                               const gchar       *str,
                               gboolean           visible_only,
                               gboolean           slice,
                               GtkTextIter       *match_start,
                               GtkTextIter       *match_end,
                               const GtkTextIter *limit)
{
  gchar **lines = NULL;
  gchar **l;
  gint n_lines;
  LinesWindow win;
  gboolean retval = FALSE;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (str != NULL, FALSE);

  if (limit &&
      gtk_text_iter_compare (limit, iter) > 0)
    return FALSE;
  
  if (*str == '\0')
    {
      /* If we can move one char, return the empty string there */
      GtkTextIter match = *iter;

      if (limit && gtk_text_iter_equal (limit, &match))
        return FALSE;
      
      if (gtk_text_iter_prev_char (&match))
        {
          if (match_start)
            *match_start = match;
          if (match_end)
            *match_end = match;
          return TRUE;
        }
      else
        return FALSE;
    }

  /* locate all lines */

  lines = strbreakup (str, "\n", -1);

  l = lines;
  n_lines = 0;
  while (*l)
    {
      ++n_lines;
      ++l;
    }

  win.n_lines = n_lines;
  win.slice = slice;
  win.visible_only = visible_only;

  lines_window_init (&win, iter);

  if (*win.lines == NULL)
    goto out;

  do
    {
      gchar *first_line_match;

      if (limit &&
          gtk_text_iter_compare (limit, &win.first_line_end) > 0)
        {
          /* We're now before the search limit, abort. */
          goto out;
        }
      
      /* If there are multiple lines, the first line will
       * end in '\n', so this will only match at the
       * end of the first line, which is correct.
       */
      first_line_match = my_strrstr (*win.lines, *lines);

      if (first_line_match &&
          vectors_equal_ignoring_trailing (lines + 1, win.lines + 1))
        {
          /* Match! */
          gint offset;
          GtkTextIter next;
          GtkTextIter start_tmp;
          
          /* Offset to start of search string */
          offset = g_utf8_strlen (*win.lines, first_line_match - *win.lines);

          next = win.first_line_start;
          start_tmp = next;
          forward_chars_with_skipping (&start_tmp, offset,
                                       visible_only, !slice);

          if (limit &&
              gtk_text_iter_compare (limit, &start_tmp) > 0)
            goto out; /* match was bogus */
          
          if (match_start)
            *match_start = start_tmp;

          /* Go to end of search string */
          l = lines;
          while (*l)
            {
              offset += g_utf8_strlen (*l, -1);
              ++l;
            }

          forward_chars_with_skipping (&next, offset,
                                       visible_only, !slice);

          if (match_end)
            *match_end = next;

          retval = TRUE;
          goto out;
        }
    }
  while (lines_window_back (&win));

 out:
  lines_window_free (&win);
  g_strfreev (lines);
  
  return retval;
}

/*
 * Comparisons
 */

gboolean
gtk_text_iter_equal (const GtkTextIter *lhs,
                     const GtkTextIter *rhs)
{
  GtkTextRealIter *real_lhs;
  GtkTextRealIter *real_rhs;

  real_lhs = (GtkTextRealIter*)lhs;
  real_rhs = (GtkTextRealIter*)rhs;

  check_invariants (lhs);
  check_invariants (rhs);

  if (real_lhs->line != real_rhs->line)
    return FALSE;
  else if (real_lhs->line_byte_offset >= 0 &&
           real_rhs->line_byte_offset >= 0)
    return real_lhs->line_byte_offset == real_rhs->line_byte_offset;
  else
    {
      /* the ensure_char_offsets () calls do nothing if the char offsets
         are already up-to-date. */
      ensure_char_offsets (real_lhs);
      ensure_char_offsets (real_rhs);
      return real_lhs->line_char_offset == real_rhs->line_char_offset;
    }
}

gint
gtk_text_iter_compare (const GtkTextIter *lhs, const GtkTextIter *rhs)
{
  GtkTextRealIter *real_lhs;
  GtkTextRealIter *real_rhs;

  real_lhs = gtk_text_iter_make_surreal (lhs);
  real_rhs = gtk_text_iter_make_surreal (rhs);

  check_invariants (lhs);
  check_invariants (rhs);

  if (real_lhs == NULL ||
      real_rhs == NULL)
    return -1; /* why not */

  if (real_lhs->line == real_rhs->line)
    {
      gint left_index, right_index;

      if (real_lhs->line_byte_offset >= 0 &&
          real_rhs->line_byte_offset >= 0)
        {
          left_index = real_lhs->line_byte_offset;
          right_index = real_rhs->line_byte_offset;
        }
      else
        {
          /* the ensure_char_offsets () calls do nothing if
             the offsets are already up-to-date. */
          ensure_char_offsets (real_lhs);
          ensure_char_offsets (real_rhs);
          left_index = real_lhs->line_char_offset;
          right_index = real_rhs->line_char_offset;
        }

      if (left_index < right_index)
        return -1;
      else if (left_index > right_index)
        return 1;
      else
        return 0;
    }
  else
    {
      gint line1, line2;

      line1 = gtk_text_iter_get_line (lhs);
      line2 = gtk_text_iter_get_line (rhs);
      if (line1 < line2)
        return -1;
      else if (line1 > line2)
        return 1;
      else
        return 0;
    }
}

gboolean
gtk_text_iter_in_range (const GtkTextIter *iter,
                        const GtkTextIter *start,
                        const GtkTextIter *end)
{
  return gtk_text_iter_compare (iter, start) >= 0 &&
    gtk_text_iter_compare (iter, end) < 0;
}

void
gtk_text_iter_reorder         (GtkTextIter *first,
                               GtkTextIter *second)
{
  g_return_if_fail (first != NULL);
  g_return_if_fail (second != NULL);

  if (gtk_text_iter_compare (first, second) > 0)
    {
      GtkTextIter tmp;

      tmp = *first;
      *first = *second;
      *second = tmp;
    }
}

/*
 * Init iterators from the BTree
 */

void
gtk_text_btree_get_iter_at_char (GtkTextBTree *tree,
                                 GtkTextIter *iter,
                                 gint char_index)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  gint real_char_index;
  gint line_start;
  GtkTextLine *line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = gtk_text_btree_get_line_at_char (tree, char_index,
                                          &line_start, &real_char_index);

  iter_init_from_char_offset (iter, tree, line, real_char_index - line_start);

  real->cached_char_index = real_char_index;

  check_invariants (iter);
}

void
gtk_text_btree_get_iter_at_line_char (GtkTextBTree *tree,
                                      GtkTextIter *iter,
                                      gint line_number,
                                      gint char_on_line)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  GtkTextLine *line;
  gint real_line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = gtk_text_btree_get_line (tree, line_number, &real_line);

  iter_init_from_char_offset (iter, tree, line, char_on_line);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  check_invariants (iter);
}

void
gtk_text_btree_get_iter_at_line_byte (GtkTextBTree   *tree,
                                      GtkTextIter    *iter,
                                      gint            line_number,
                                      gint            byte_index)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;
  GtkTextLine *line;
  gint real_line;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  line = gtk_text_btree_get_line (tree, line_number, &real_line);

  iter_init_from_byte_offset (iter, tree, line, byte_index);

  /* We might as well cache this, since we know it. */
  real->cached_line_number = real_line;

  if (real->segment->type == &gtk_text_char_type &&
      (real->segment->body.chars[real->segment_byte_offset] & 0xc0) == 0x80)
    g_warning ("%s: Incorrect byte offset %d falls in the middle of a UTF-8 "
               "character; this will crash the text buffer. "
               "Byte indexes must refer to the start of a character.",
               G_STRLOC, byte_index);

  check_invariants (iter);
}

void
gtk_text_btree_get_iter_at_line      (GtkTextBTree   *tree,
                                      GtkTextIter    *iter,
                                      GtkTextLine    *line,
                                      gint            byte_offset)
{
  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (line != NULL);

  iter_init_from_byte_offset (iter, tree, line, byte_offset);

  check_invariants (iter);
}

gboolean
gtk_text_btree_get_iter_at_first_toggle (GtkTextBTree   *tree,
                                         GtkTextIter    *iter,
                                         GtkTextTag     *tag)
{
  GtkTextLine *line;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  line = gtk_text_btree_first_could_contain_tag (tree, tag);

  if (line == NULL)
    {
      /* Set iter to last in tree */
      gtk_text_btree_get_last_iter (tree, iter);
      check_invariants (iter);
      return FALSE;
    }
  else
    {
      iter_init_from_byte_offset (iter, tree, line, 0);
      gtk_text_iter_forward_to_tag_toggle (iter, tag);
      check_invariants (iter);
      return TRUE;
    }
}

gboolean
gtk_text_btree_get_iter_at_last_toggle  (GtkTextBTree   *tree,
                                         GtkTextIter    *iter,
                                         GtkTextTag     *tag)
{
  GtkTextLine *line;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  line = gtk_text_btree_last_could_contain_tag (tree, tag);

  if (line == NULL)
    {
      /* Set iter to first in tree */
      gtk_text_btree_get_iter_at_line_char (tree, iter, 0, 0);
      check_invariants (iter);
      return FALSE;
    }
  else
    {
      iter_init_from_byte_offset (iter, tree, line, -1);
      gtk_text_iter_backward_to_tag_toggle (iter, tag);
      check_invariants (iter);
      return TRUE;
    }
}

gboolean
gtk_text_btree_get_iter_at_mark_name (GtkTextBTree *tree,
                                      GtkTextIter *iter,
                                      const gchar *mark_name)
{
  GtkTextMark *mark;

  g_return_val_if_fail (iter != NULL, FALSE);
  g_return_val_if_fail (tree != NULL, FALSE);

  mark = gtk_text_btree_get_mark_by_name (tree, mark_name);

  if (mark == NULL)
    return FALSE;
  else
    {
      gtk_text_btree_get_iter_at_mark (tree, iter, mark);
      check_invariants (iter);
      return TRUE;
    }
}

void
gtk_text_btree_get_iter_at_mark (GtkTextBTree *tree,
                                 GtkTextIter *iter,
                                 GtkTextMark *mark)
{
  GtkTextLineSegment *seg;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (GTK_IS_TEXT_MARK (mark));

  seg = mark->segment;

  iter_init_from_segment (iter, tree,
                          seg->body.mark.line, seg);
  g_assert (seg->body.mark.line == gtk_text_iter_get_text_line (iter));
  check_invariants (iter);
}

void
gtk_text_btree_get_iter_at_child_anchor (GtkTextBTree       *tree,
                                         GtkTextIter        *iter,
                                         GtkTextChildAnchor *anchor)
{
  GtkTextLineSegment *seg;

  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);
  g_return_if_fail (GTK_IS_TEXT_CHILD_ANCHOR (anchor));

  seg = anchor->segment;
  
  iter_init_from_segment (iter, tree,
                          seg->body.child.line, seg);
  g_assert (seg->body.child.line == gtk_text_iter_get_text_line (iter));
  check_invariants (iter);
}

void
gtk_text_btree_get_last_iter         (GtkTextBTree   *tree,
                                      GtkTextIter    *iter)
{
  g_return_if_fail (iter != NULL);
  g_return_if_fail (tree != NULL);

  gtk_text_btree_get_iter_at_char (tree,
                                   iter,
                                   gtk_text_btree_char_count (tree));
  check_invariants (iter);
}

void
gtk_text_iter_spew (const GtkTextIter *iter, const gchar *desc)
{
  GtkTextRealIter *real = (GtkTextRealIter*)iter;

  g_return_if_fail (iter != NULL);

  if (real->chars_changed_stamp != gtk_text_btree_get_chars_changed_stamp (real->tree))
    g_print (" %20s: <invalidated iterator>\n", desc);
  else
    {
      check_invariants (iter);
      g_print (" %20s: line %d / char %d / line char %d / line byte %d\n",
               desc,
               gtk_text_iter_get_line (iter),
               gtk_text_iter_get_offset (iter),
               gtk_text_iter_get_line_offset (iter),
               gtk_text_iter_get_line_index (iter));
      check_invariants (iter);
    }
}

void
gtk_text_iter_check (const GtkTextIter *iter)
{
  const GtkTextRealIter *real = (const GtkTextRealIter*)iter;
  gint line_char_offset, line_byte_offset, seg_char_offset, seg_byte_offset;
  GtkTextLineSegment *byte_segment = NULL;
  GtkTextLineSegment *byte_any_segment = NULL;
  GtkTextLineSegment *char_segment = NULL;
  GtkTextLineSegment *char_any_segment = NULL;
  gboolean segments_updated;

  /* This function checks our class invariants for the Iter class. */

  g_assert (sizeof (GtkTextIter) == sizeof (GtkTextRealIter));

  if (real->chars_changed_stamp !=
      gtk_text_btree_get_chars_changed_stamp (real->tree))
    g_error ("iterator check failed: invalid iterator");

  if (real->line_char_offset < 0 && real->line_byte_offset < 0)
    g_error ("iterator check failed: both char and byte offsets are invalid");

  segments_updated = (real->segments_changed_stamp ==
                      gtk_text_btree_get_segments_changed_stamp (real->tree));

#if 0
  printf ("checking iter, segments %s updated, byte %d char %d\n",
          segments_updated ? "are" : "aren't",
          real->line_byte_offset,
          real->line_char_offset);
#endif

  if (segments_updated)
    {
      if (real->segment_char_offset < 0 && real->segment_byte_offset < 0)
        g_error ("iterator check failed: both char and byte segment offsets are invalid");

      if (real->segment->char_count == 0)
        g_error ("iterator check failed: segment is not indexable.");

      if (real->line_char_offset >= 0 && real->segment_char_offset < 0)
        g_error ("segment char offset is not properly up-to-date");

      if (real->line_byte_offset >= 0 && real->segment_byte_offset < 0)
        g_error ("segment byte offset is not properly up-to-date");

      if (real->segment_byte_offset >= 0 &&
          real->segment_byte_offset >= real->segment->byte_count)
        g_error ("segment byte offset is too large.");

      if (real->segment_char_offset >= 0 &&
          real->segment_char_offset >= real->segment->char_count)
        g_error ("segment char offset is too large.");
    }

  if (real->line_byte_offset >= 0)
    {
      gtk_text_line_byte_locate (real->line, real->line_byte_offset,
                                 &byte_segment, &byte_any_segment,
                                 &seg_byte_offset, &line_byte_offset);

      if (line_byte_offset != real->line_byte_offset)
        g_error ("wrong byte offset was stored in iterator");

      if (segments_updated)
        {
          if (real->segment != byte_segment)
            g_error ("wrong segment was stored in iterator");

          if (real->any_segment != byte_any_segment)
            g_error ("wrong any_segment was stored in iterator");

          if (seg_byte_offset != real->segment_byte_offset)
            g_error ("wrong segment byte offset was stored in iterator");

          if (byte_segment->type == &gtk_text_char_type)
            {
              const gchar *p;
              p = byte_segment->body.chars + seg_byte_offset;
              
              if (!gtk_text_byte_begins_utf8_char (p))
                g_error ("broken iterator byte index pointed into the middle of a character");
            }
        }
    }

  if (real->line_char_offset >= 0)
    {
      gtk_text_line_char_locate (real->line, real->line_char_offset,
                                 &char_segment, &char_any_segment,
                                 &seg_char_offset, &line_char_offset);

      if (line_char_offset != real->line_char_offset)
        g_error ("wrong char offset was stored in iterator");

      if (segments_updated)
        {          
          if (real->segment != char_segment)
            g_error ("wrong segment was stored in iterator");

          if (real->any_segment != char_any_segment)
            g_error ("wrong any_segment was stored in iterator");

          if (seg_char_offset != real->segment_char_offset)
            g_error ("wrong segment char offset was stored in iterator");

          if (char_segment->type == &gtk_text_char_type)
            {
              const gchar *p;
              p = g_utf8_offset_to_pointer (char_segment->body.chars,
                                            seg_char_offset);

              /* hmm, not likely to happen eh */
              if (!gtk_text_byte_begins_utf8_char (p))
                g_error ("broken iterator char offset pointed into the middle of a character");
            }
        }
    }

  if (real->line_char_offset >= 0 && real->line_byte_offset >= 0)
    {
      if (byte_segment != char_segment)
        g_error ("char and byte offsets did not point to the same segment");

      if (byte_any_segment != char_any_segment)
        g_error ("char and byte offsets did not point to the same any segment");

      /* Make sure the segment offsets are equivalent, if it's a char
         segment. */
      if (char_segment->type == &gtk_text_char_type)
        {
          gint byte_offset = 0;
          gint char_offset = 0;
          while (char_offset < seg_char_offset)
            {
              const char * start = char_segment->body.chars + byte_offset;
              byte_offset += g_utf8_next_char (start) - start;
              char_offset += 1;
            }

          if (byte_offset != seg_byte_offset)
            g_error ("byte offset did not correspond to char offset");

          char_offset =
            g_utf8_strlen (char_segment->body.chars, seg_byte_offset);

          if (char_offset != seg_char_offset)
            g_error ("char offset did not correspond to byte offset");

          if (!gtk_text_byte_begins_utf8_char (char_segment->body.chars + seg_byte_offset))
            g_error ("byte index for iterator does not index the start of a character");
        }
    }

  if (real->cached_line_number >= 0)
    {
      gint should_be;

      should_be = gtk_text_line_get_number (real->line);
      if (real->cached_line_number != should_be)
        g_error ("wrong line number was cached");
    }

  if (real->cached_char_index >= 0)
    {
      if (real->line_char_offset >= 0) /* only way we can check it
                                          efficiently, not a real
                                          invariant. */
        {
          gint char_index;

          char_index = gtk_text_line_char_index (real->line);
          char_index += real->line_char_offset;

          if (real->cached_char_index != char_index)
            g_error ("wrong char index was cached");
        }
    }
}